The present invention relates to an electric heating element of the radiant type, as used in particular, although not solely, in electric cooking tops.
More specifically, the present invention refers to an electric heating element in the shape of an elongated strip of an electrically resistive material, such as metals or special alloys thereof, which is arranged upon or partially inserted in a base of electrically insulating and thermally insulating (refractory) material, and is secured to the base by means of appropriate fastening means.
The present invention also relates to a heating plate, or hotplate, in particular of the type used in household cooking tops provided with an upper smooth glass-ceramic surface, equipped with a radiant heating element according to the present invention.
As far as the prior art is concerned, along with the related drawbacks and particular features, this is described in the Italian patent application no. PN2001U000016 filed by this same Applicant, to which reference should therefore be made for reasons of brevity.
The above cited document describes a coiled heating element that is secured in various manners to the related base of insulating material; the technical solution proposed in the patent application has proven particularly advantageous in view of the easiness and inexpensiveness ensured by it in both manufacturing the resistive strip and applying it to the radiant hotplate. However, it has also turned up some drawbacks connected with the heat distortion effect that is brought about by the temperature difference that comes to exist between the zones inside or close to the insulating base and the zones outside or far therefrom. Such a problem may even cause the heating element to partially slip out of the recesses in the base in which it is inserted, under easily imaginable negative consequences from both a functional and an aesthetical point of view.
Based on the foregoing considerations, it therefore is a purpose of the present invention to provide a kind of electric heating element of the radiant type, which makes use of a corrugated resistive strip provided with straight attachment pins, and which enables the radiating surface to be maximized while doing away with the above cited heat distortion drawbacks and the mechanical stresses associated therewith.
These aims, along with further features of the present invention, are reached in radiant-type electric heating elements of the kind made and operating in accordance with the characteristics recited in the appended claims.
The present invention can be implemented according to a preferred, however not sole embodiment thereof, which will be described in detail and illustrated below by mere way of non-limiting example with reference to the accompanying drawings, in which:
With reference to the figures, a radiant-type hotplate according to the present invention substantially comprises:
According to the present invention, the electric heating elements 5 are obtained out of an elongated flat strip, as it will referred to hereinafter, of an electrically resistive material, preferably a metal or alloys thereof.
The flat strip of resistive material is shaped in a corrugated or a saw-toothed manner according to different patterns or variants, which, however, share in all cases the feature according to which the two opposite edges of the strip are so shaped as to come to lie on two distinct respective planes, the two planes being parallel to each other.
A further basic feature shared by all the above mentioned possible variants in the shaping of the strip is given by the fact that such a strip is formed by a sequence of planar (flat) lengths and curved lengths, in which the different lengths are mutually alternated, and in which the curved lengths are curved either in a sharp manner, so as to confer a saw-toothed profile to the strip, or with a more smooth, continuous curvature along a short length of the flat strip.
Furthermore, at least some of the planar lengths are connected to respective appendices that are at least partially inserted in the base of insulating material 1, in which the appendices are connected to a same edge of the respective flat strip.
With reference to the figures, these can be noticed to represent some embodiments of the resistive flat strip according to the present invention. In particular, it can be noticed that
According to the present invention, the planar length 28 is provided with a planar anchorage appendix 29, which is coplanar with the planar length 28 and is adapted to engage the base 1 by being inserted therein, as this is illustrated in
A different embodiment is illustrated in
A third embodiment is illustrated in
Similarly to the aforementioned case, this solution can be noticed to show the planar appendix 49 being, in turn, provided with two further side planar appendices 491 and 492 located at the opposite free edges thereof and oriented in a manner so as to be non-coplanar with, but rather orthogonal to the respective planar appendix 49.
As far as the assembly arrangement thereof is concerned, the resistive strip is mounted in such a manner as to cause the tips to lie in a position that is not orthogonal to the surface of the base 1, but are alternately resting thereupon or are slightly inserted therein, so that the free tips 41 and 44 lie above the surface W of the insulating base 1. In this manner, the respective planar length 48 comes to lie fully parallel to and adhere against the surface of the base 1. Also in this case, both the planar appendix 49 and the two further side appendices 491 and 492 are capable of being inserted edgeways in the base 1.
Preferably, as is shown in
However, the above illustrated technical solutions, although quite effective and easily implemented, have following drawback in the real practice. Since there are provided both corrugated resistive lengths and planar resistive lengths, the presence of the last mentioned lengths imposes, for a same total power output, a heating element that is “longer” than it would actually be if it were formed by only a single corrugated length. From this fact, the need therefore arises for the flat resistive strip to be wound with a greater number of turns or bends, which would, of course, become too thick, i.e., too closely packed, and this would bring problems with it from both a manufacturing and a functional point of view.
In view of dealing with such a drawback, and with reference to
In correspondence to the planar walls, and on the same edge facing the insulating base 1, there are applied respective appendices 501, 511, 521, etc., which, similarly to the aforementioned cases, are inserted edgeways into the insulating base, and which ensure the stability of the related flat resistive strip when the latter is applied to the base with the planar lengths 50, 51, 52, etc. arranged orthogonally thereto.
Such a conformation allows for following two variants. The first one of these variants is based on the fact that the anchoring appendices 501, 502, 503 are joined to respective planar walls 50, 51, 52 . . . that follow each other, i.e., are arranged successively with respect to each other, as is best illustrated in
It has, however, been noticed that the aforementioned solutions, based on appendices joined to the flat resistive strip over the whole width of the appendices and, therefore, over rather extended lengths, lead, as an obvious result, to a modification and, more precisely, a reduction in the ohmic resistance in correspondence thereof. Since a rather high current is actually supplied, such a reduction in the electric resistance translates into a corresponding reduction in the power output along the lengths, and this of course leads to the ultimate result of a decay in the overall performance of the hotplate, a much slower temperature rise pattern and also a quicker weardown brought about by the different thermal expansion pattern determined by the different heat outputs occurring along contiguous lengths of the strip.
In order to deal with such drawbacks, and with particular reference to
The particularity of this invention lies in the fact that the width d1 of the joining means 9, which are preferably constituted by metal links that are punched integrally with the flat resistive strip, is substantially smaller than the length D of the entire appendix, so that the ohmic resistance of the flat resistive strip is not altered to any significant extent, while still ensuring good mechanical securing and holding properties owing to the width of the portion of appendix that is inserted in the insulating base remaining almost the same.
In the course of laboratory tests and experiments, which have been carried out by placing the appendix 19 illustrated in
The results of these tests are summarized in the thermographies illustrated in
All other characteristics are specifications of the specimens are similar and, in particular, h=1.2 mm.
From the above cited thermographies, it clearly appears that, with d1=0.5 mm, the thermal behavior of the related lengths of corrugated heating element is not altered to any appreciable extent.
Such behavior is confirmed by the following measurements described with reference to
It fully and clearly appears that, as these joining means become thinner, the temperature difference between the above-mentioned zones progressively decreases down to almost zero, which further demonstrates that the presence of appendices of the herein described kind may not affect the thermal behavior of a corrugated heating element according to the present invention to any extent whatsoever. It should furthermore be noticed that it is preferable if such joining means are formed with a rectangular shape (
It has also been considered that the exiguity of the width of the joining means 9 used to unite the appendix 19 to the flat resistive strip 5 might lead to an undesired weakening thereof. Therefore, in view of doing away with such a risk, the following advantageous variant is proposed. With reference to
The advantageous result is thereby attained that the planar appendices 29A, although provided with the perforation 99, constitute neither a weakening factor nor a cause of uncertain securing of the resistive strip 5 to the base of insulating material 1, while the perforations 99 are on the contrary adequate for reducing the width of the common section 100 to a desired extent, so that the electric behavior of the planar appendices 29A and the corresponding lengths of flat resistive strip 5 resembles in an almost indistinguishable and, therefore, advantageous manner the behavior of the appendices of the kind illustrated in
It will also be readily appreciated that the solution calling for the appropriate perforations 99 to be provided in respective planar appendices can also be favorably applied to all variants and embodiments of the types of planar appendices illustrated in
Number | Date | Country | Kind |
---|---|---|---|
PN20010045 U | Nov 2001 | IT | national |
Filing Document | Filing Date | Country | Kind | 371c Date |
---|---|---|---|---|
PCT/EP02/11495 | 10/15/2002 | WO | 00 | 8/22/2005 |
Publishing Document | Publishing Date | Country | Kind |
---|---|---|---|
WO03/045112 | 5/30/2003 | WO | A |
Number | Name | Date | Kind |
---|---|---|---|
4161648 | Goessler | Jul 1979 | A |
5477031 | McWilliams | Dec 1995 | A |
5753892 | Gross et al. | May 1998 | A |
5796075 | Gross et al. | Aug 1998 | A |
5837975 | Dillard et al. | Nov 1998 | A |
6207935 | Dittmar et al. | Mar 2001 | B1 |
Number | Date | Country |
---|---|---|
0625865 | Nov 1994 | EP |
Number | Date | Country | |
---|---|---|---|
20060151472 A1 | Jul 2006 | US |